Myasthenia gravis (my-us-THEE-nee-uh GRAY-vis) is characterized by weakness and rapid fatigue of any of the muscles under your voluntary control.

Myasthenia gravis is caused by a breakdown in the normal communication between nerves and muscles.

There is no cure for myasthenia gravis, but treatment can help relieve signs and symptoms, such as weakness of arm or leg muscles, double vision, drooping eyelids, and difficulties with speech, chewing, swallowing and breathing.

Though myasthenia gravis can affect people of any age, it's more common in women younger than 40 and in men older than 60.

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